A coupled microphysical/radiative transfer model of albedo and emissivity of planetary surfaces covered by volatile ices     

Janusz Eluszkiewicz  Jean-Luc Moncet 《Icarus》2003,166(2):375-384

A new model of albedo and emissivity of planetary surfaces covered by volatile ices in the form of porous slab-like deposits is described. In the model, a radiative transfer model is coupled with a microphysical model in order to link changes in albedo and emissivity to changes in porosity caused by ice metamorphism. Preliminary results for Triton, Pluto, and Io are presented (the martian CO₂ caps will be the subject of a separate publication). The coupled model will aid in the interpretation of ground-based and spacecraft observations and should lead to advances in surface and atmospheric modeling.  相似文献   

Longevity of fluorine-bearing tremolite on Venus     

Natasha M. Johnson  Bruce Fegley Jr. 《Icarus》2003,165(2):340-348

There is a general belief that hydrous minerals cannot exist on Venus under current surface conditions. This view was challenged when Johnson and Fegley (2000, Icarus 146, 301-306) showed that tremolite (Ca₂Mg₅Si₈O₂₂(OH)₂), a hydrous mineral, is stable against thermal decomposition at current Venus surface temperatures, e.g., 50% decomposition in 4 Ga at 740 K. To further explore hydrous mineral thermal stability on Venus, we experimentally determined the thermal decomposition kinetics of fluorine-bearing tremolite. Fluor-tremolite is thermodynamically more stable than OH-tremolite and should decompose more slowly. However how much slower was unknown. We measured the decomposition rate of fluorine-bearing tremolite and show that its decomposition is several times to greater than ten times slower than that of OH-tremolite. We also show that F-bearing tremolite is depleted in fluorine after decomposition and that fluorine is lost as a volatile species such as HF gas. If tremolite ever formed on Venus, it would probably also contain fluorine. The exceptional stability of F-bearing tremolite strengthens our conclusions that if hydrous minerals ever formed on Venus, they could still be there today.  相似文献   

Analytical solutions of one‐dimensional infiltration before and after ponding     

Jiann‐Mou Chen  Yih‐Chi Tan  Chu‐Hui Chen 《水文研究》2003,17(4):815-822

This paper is a continuation of previous research, which obtained a convenient solution for arbitrary surface fluxes before ponding. By means of Fourier Transformation this has been extended to derive analytical solutions of a linearized Richards' equation for arbitrary input fluxes after surface saturation. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

NEMERTEANS OF ZHOUSHAN ISLANDS, EAST CHINA SEA COAST,CHINA Ⅰ.ENOPLA: DISTROMATOPHYNCHOCOELA: MONOSTILIFERA: EMPLECTONEMERTIDAE     

孙世春 《中国海洋湖沼学报》1995,(2)

Two nemerteans of the Zhoushan Islands, Paranemertes sinensis sp. nov. and P. peregrina, are reportedin this paper. P. sinensis sp. nov. has the body wall longitudinal musculature anteriorly divided,numerous eyes grouped into four clusters, two pairs of cephalic furrows, rhynchocoel 1/3 to 1/2 of fullbody length, cephalic glands well developed and posteriorly extending beyond the cerebral ganglia.precerebral septum absent, cerebral sense organs situated in front of brain, three pairs of nephridiopores,and 17-18 proboscis nerves.  相似文献   

Reliability assessment of serviceability performance of braced retaining walls using a neural network approach     

A. T. C. Goh  F. H. Kulhawy 《国际地质力学数值与分析法杂志》2005,29(6):627-642

In urban environments, one major concern with deep excavations in soft clay is the potentially large ground deformations in and around the excavation. Excessive movements can damage adjacent buildings and utilities. There are many uncertainties associated with the calculation of the ultimate or serviceability performance of a braced excavation system. These include the variabilities of the loadings, geotechnical soil properties, and engineering and geometrical properties of the wall. A risk‐based approach to serviceability performance failure is necessary to incorporate systematically the uncertainties associated with the various design parameters. This paper demonstrates the use of an integrated neural network–reliability method to assess the risk of serviceability failure through the calculation of the reliability index. By first performing a series of parametric studies using the finite element method and then approximating the non‐linear limit state surface (the boundary separating the safe and ‘failure’ domains) through a neural network model, the reliability index can be determined with the aid of a spreadsheet. Two illustrative examples are presented to show how the serviceability performance for braced excavation problems can be assessed using the reliability index. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Fresnel modeling of hematite crystal surfaces and application to martian hematite spherules     

Timothy D. Glotch  Philip R. Christensen  Thomas G. Sharp 《Icarus》2006,181(2):408-418

The gray crystalline hematite at Meridiani Planum first discovered by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) instrument occurs as spherules that have been interpreted as concretions. Analysis of the TES and mini-TES spectra shows that no 390 cm⁻¹ feature is present in the characteristic martian hematite spectrum. Here, we incorporate the mid-IR optical constants of hematite into a simple Fresnel reflectance model to understand the effect of emission angle and crystal morphology on the presence or absence of the 390 cm⁻¹ feature in an IR hematite spectrum. Based on the results we offer two models for the internal structure of the martian hematite spherules.  相似文献   

Experimental study on the deterioration and natural remediation of the Ariake Sea tidal mud caused by the sea laver treatment acid practice and the upward seepage of pore water liquid     

Yan-Jun Du  Song-Yu Liu  Shigenori Hayashi 《Environmental Geology》2008,55(4):889-900

This study presents a laboratory study of the following two aspects: (1) the influence of sea laver treatment acid on the geoenvironmental properties of Ariake Sea tidal mud, and (2) the natural remediation effect on the sea laver treatment acid contaminated Ariake Sea tidal mud caused by the upward seepage of pore water liquid in the mud. Firstly, the mechanisms of the transport of sea laver treatment acid in the Ariake Sea tidal mud and the generation mechanisms of the upward seepage flow in the Ariake Sea tidal mud are discussed. Secondly, a series of one-dimensional laboratory infiltration tests were carried out to investigate the deterioration of the Ariake Sea tidal mud caused by the sea laver acid treatment practice. Test results reveal that the acid treatment practice caused considerable change in the geochemical properties of the mud in terms of increase in sulfide content and decrease in pH value. After the treatment by the sea laver treatment acid, the sulfide content of the mud even exceeded the safe limit value for the benthos, which represents undesirable living condition for benthos. Thirdly, series of laboratory fresh seawater infiltration tests for the deteriorated Iida site mud were conducted to illustrate this natural remediation efficiency. It is found that with the infiltration of the fresh seawater, the sulfide content of the Iida site mud was considerably reduced and pH value increased to an acceptable range for benthos living in the tidal flat mud. With the increase in the infiltration time and the hydraulic gradient, the remediation efficiency could be increased.  相似文献   

Geotechnical properties of evaporite soils of the Dead Sea area     

Sam Frydman  Josef Charrach  Ian Goretsky 《Engineering Geology》2008,101(3-4):236-244

The Dead Sea Basin is the lowest point on earth and is tectonically subsiding. During the Holocene Period the climate became much drier with increasing evaporation whereby initially lacustrine sediments were deposited from the non-marine brines, giving a multi-layered stratigraphy of lime carbonate and halite sediments. The lime carbonate sediments are comprised of laminated, clay to silt sized, clastic sediments (calcite) and authigenic aragonite and gypsum. The halite commonly appears as rock salt. Chemical industries, based on harvesting the salts from the Dead Sea, have developed on both the Israeli and the Jordanian sides of the basin. The lime carbonate soils are used for dike construction, and these soils, together with significant salt layers, are encountered in the foundations of structures, dikes, and tailings dams, requiring definition of their geotechnical properties. Use of standard soil mechanics definitions and testing approaches for the lime carbonates have been found inapplicable, particularly in view of their exceptionally high saline content, and it has been necessary to develop new concepts. The rock salt is encountered at shallow depths, with unit weights considerably lower than those usually discussed in the literature, and with correspondingly different mechanical properties. The geotechnical properties of these soils, and approaches used to define them, are discussed in the paper.  相似文献   

Planktonic foraminifers in the southern Bering Sea: Changes in composition and productivity during the Late Pleistocene-Holocene     

M. P. Chekhovskaya  I. A. Basov  A. G. Matul  T. A. Khusid  S. A. Gorbarenko 《Stratigraphy and Geological Correlation》2008,16(3):328-342

Taxonomic composition and distribution of planktonic foraminifers are studied in section of Core GC-11 that penetrated through Upper Quaternary sediments of the Bowers Ridge western slope, the southern Bering Sea. As is shown, structure of foraminiferal assemblage and productivity have varied substantially during the last 32000 calendar years in response to changes in surface water temperatures and water mass circulation in the northern part of the Pacific, the Bering Sea included. The productivity was maximal during deglaciation epoch, being notably lower in the Holocene and minimal at the glaciation time.  相似文献   

南海东北部下地壳高速层的成因探讨   总被引：2，自引：0，他引：2  

刘安  武国忠  吴世敏 《地质论评》2008,54(5):609-616

通过对南海北部大陆边缘地壳结构分析,指出南海东北部存在下地壳高速层,大致分布在112°E~120°E,19°N~22°N的陆坡和拉张程度大的陆架地区,呈NEE向延伸,在海底地震仪剖面上最大的厚度有8km,向南海海盆方向减薄。通过对比综合分析认为,高速层物质组成是底侵作用形成的熔岩垫,由于伸展作用,南海海底扩张（30Ma）前后底侵作用形成了熔岩垫,并促使南海北部大陆边缘地壳抬升,导致区域性抬升剥蚀。  相似文献